I been a TIG hobbyist for about 7 years, when I bought my Miller 180SD Syncrowave new. Through the years I've occasionally come up against both the high and low limits of the machine, and have always dreamed of finding a used 250 Syncro on the cheap.
Well, I found a non-working 350 Syncro of 1990 vintage for cheap, brought it home, cleaned it up, eventually found the problem (about $2 worth of components on PC1; a shorted tantalum cap that took out a couple of resistors and a PCB trace). Fan was noisy, put new bearings in the motor.
It now runs like a champ. Looks nice, welds nice. Plus it has the built-in pulser option, so I'm pretty happy now. My 180SD has been a great unit, but it's time for it to go to a new home.....
My largest torch today is a 17 aircooled, so I'm planning to get both18 and 20 watercooled torches. Over the weekend, I found a good used Miller Coolmate 3 for sale and brought it home.
So I started researching the whole coolant issue on this NG and other forums. I wasn't aware when I bought the Coolmate of the pricey Miller low-conductivity coolant ($30 a gallon! and I need 3 gals for the Coolmate!)
So I started researching the various options. To sum up what I've found, some folks just hook up to flowing tap water, some use distilled water with their coolers if their keeping the unit in a warm shop, some use the pink RV Propylene Glycol stuff, some use ordinary auto antifreeze.(ethylene glycol mixes)
Obviously, Miller thinks that low conductivity is important. And it would seem to me that if your coolant is conductive, then you will lose strength of the HF. I have found no data on relative conductivity of various solutions, so tonight I rigged up a "kitchen experiment", pretty non-scientific from an absolute sense, but pretty good from a relative sense to check relative conductivity of various solutions.
I went to Wally World today and picked up a gallon of Distilled Water, a gallon of Prestone RV antifreeze, a gallon of Dow pink Dowfrost RV antifreeze. I already had a gallon of Zerex auto antifreeze and a few quarts of Pentosin Pink antifreeze in the garage.
I made a simple conductivity divider with a set of known resistances, and used 240VAC as the excitation voltage. (yes; I know that the high voltage of the HF output can have different conductivity characteristcs, but I wasn't going to mess with any higher voltage)
I constructed a simple conductivity cell with a glass beaker and a couple of stainless steel butter knives from the kitchen. (to keep with the "kitchen experiment" theme, of course)
I then used my Fluke 179 DMM to measure the voltage across the cell with various liquids in the cell. A pefect insulator would measure240 VAC (actually 236 VAC according to my meter), a dead short would be 0 VAC. I rinsed out the beaker with distilled water between liquids.
Here's my findings:
Distilled Water: 42 VAC Hard well tap water : 700 millivolts AC Soft well tap water: 600 millivolts AC Prestone RV antifreeze: 115 millivolts AC Dow RV antifreeze: 175 millivolts AC Pentosin/Distilled 50%: 600 millivolts AC Zerex/distilled 50%: 550 millivolts AC
I investigated the theoretical conductivities of industrial ethylene and propylene glycol aqueous mixtures, and both should be in the range of near distilled water; around 5 micromhos/cm. I also found data that the Dow RV stuff has a conductivity about 2,000 micromhos/cm, or400 times that of distilled water. This is close to what I observed. Obviously, both the RV and auto additives make the mixtures dramatically more conductive than the base water and glycol mixes. I've seen several assumptions in this NG that Miller doesn't recommend auto antifreeze because of stop leak additives. I think they don't recommend it because the damn stuff is so conductive....
Conclusions? Obviously distilled water is the way to go, but what about if you need freeze protection? (my shop isn't heated full time; rarely gets below freezing, but has a few times in the past) I would NEVER use the pink RV stuff of any brand. It is basically a dead short path for the HF back to your cooler. Tap water is much better, (my tap water, anyway. YMMV) Automotive stuff is marginally better. None of these are any good, really (IMHO.)
Here's my plan. I need 3 gallons for my system. The Miller low conductivity stuff would set me back $90. I have found several sources for both Propylene and Ethylene Glycol (industrial grade) for about $30 a gallon. I can easily get by with a 33% mixture for my shop, which will cost about $32 total, a $60 savings.
Here's a question to those running either tap water or especially pink RV stuff: Have you noticed a degradation of HF power, from conduction losses? Given my observations, it appears to me that you should. (Or perhaps suffer poor component life in your welder's HF circuitry?)